U.S. patent number 6,198,049 [Application Number 08/571,323] was granted by the patent office on 2001-03-06 for torque limiting socket for twist-on wire connectors.
This patent grant is currently assigned to GB Electric, Inc.. Invention is credited to Chris W. Korinek.
United States Patent |
6,198,049 |
Korinek |
March 6, 2001 |
Torque limiting socket for twist-on wire connectors
Abstract
Ends of several electrical wires are joined by a connector which
is twisted onto the wire to a predefined torque level by using a
unique tool socket. The connector has a body with closed end and an
open end for receiving the electrical wires. At least a portion of
the hollow body has an equilateral polygonal cross section shape
formed by side surfaces which meet at corner sections. The tool
socket includes a coupling through which torque is applied and has
an aperture for receiving the connector. The aperture has a
cross-sectional shape such that the tool socket engages only the
connector corner sections and a space exists between the connector
side surfaces and the socket. That engagement concentrates torque
applied by the tool socket to the connector which causes the corner
sections to round upon application of more than the predefined
torque level, thus preventing excessive torque from being applied
to the connector and the wires.
Inventors: |
Korinek; Chris W. (Cedarburg,
WI) |
Assignee: |
GB Electric, Inc. (Milwaukee,
WI)
|
Family
ID: |
24283217 |
Appl.
No.: |
08/571,323 |
Filed: |
December 12, 1995 |
Current U.S.
Class: |
174/87; 7/107;
81/121.1; 81/124.3 |
Current CPC
Class: |
B25B
23/1415 (20130101); B25B 23/142 (20130101); F16B
31/027 (20130101); H01R 4/22 (20130101) |
Current International
Class: |
B25B
23/142 (20060101); B25B 23/14 (20060101); F16B
31/00 (20060101); F16B 31/02 (20060101); H01R
4/22 (20060101); H01R 4/00 (20060101); H01R
004/22 () |
Field of
Search: |
;174/87,84S ;29/758
;7/107 ;81/121.1,124.3,122,431 ;D13/150 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kincaid; Kristine
Assistant Examiner: Nguyen; Chau N.
Attorney, Agent or Firm: Quarles & Brady Haas; George
E.
Claims
I claim:
1. A system for joining ends of electrical wires to a predefined
torque level, which comprises:
a connector having a hollow body with an open end, a closed end and
an outer surface extending between the open and closed ends, and at
least a portion of the outer surface having elements which form a
cross section with a polygonal shape; and
a tool socket having a mechanism by which torque is applied to the
tool socket, and having an aperture within which is removably
received the closed end of the connector with side walls of the
aperture engaging the portion of the outer surface, the aperture
being larger in cross section than the connector so that a gap
exists between the side walls and the outer surface, as a result of
the gap the elements of the connector deform when the tool socket
applies greater than the predefined torque level to the
connector;
wherein the gap defines the predefined torque level which is great
enough for the connector to establish a safe electrical connection
between the wires, and is less than a torque level at which damage
to the wires or to the connector occurs.
2. The system as recited in claim 1 wherein the portion of the
outer surface has a cross section with an equilateral polygonal
shape with corner sections.
3. The system as recited in claim 2 wherein the aperture of the
tool socket has a cross section with an equilateral polygonal shape
with corners.
4. The system as recited in claim 3 wherein upon application of
torque, the corners of the tool rotate out of engagement with the
corner sections of the connector.
5. The system as recited in claim 2 wherein the aperture of the
tool socket has a cross section with the equilateral polygonal
shape formed by a plurality of side walls, each side wall abutting
adjacent ones of the side walls at two of the corners of the
polygonal shape and having an intermediate section between the two
of the corners in which the intermediate section is spaced from the
connector received in the aperture.
6. The system as recited in claim 1 wherein the portion of the
connector has a hexagonal cross section; and the aperture of the
tool socket has a hexagonal cross section.
7. The system as recited in claim 1 wherein the portion of the
connector has a hexagonal cross section; and the aperture of the
tool socket has a dodecagonal cross section.
Description
BACKGROUND OF THE INVENTION
The present invention relates to connecting electrical wires with
twist-on type connectors; and more particularly, to tools for
fastening such connectors.
The ends of two or more wires of an electrical circuit are often
connected together using a twist-on type wire connector. These
connectors are available in a variety of sizes and shapes and
commonly have a conical shaped body of insulating material, such as
plastic, with an opening at the larger end. The opening
communicates with a tapered aperture which has helical threads cut
in the interior surface of the body. The fastening operation is
performed by inserting the stripped ends of two or more wires into
the open end and rotating the connector so that the threads screw
onto and twist the wires together to form an electrical coupling.
An improved connector has a tapered metal spring inserted into the
aperture of the insulating body. The spring engages the bare wires
and aids in providing a conductive path there between.
Twist-on type wire connectors frequently are used by electricians
to connect two or more wires in a junction box within a building.
In this application, electricians typically twist on the connectors
by hand, although manual tools, such as a hexagonal socket wrench
or a nut driver, can be used. These connectors also are employed in
a variety of electrical appliances. For example, connections
between the wires of a ballast in a fluorescent lighting fixture
and the electrical supply cord are made in this manner. In a
factory, the wire connectors often are attached using a
pneumatically or electrically powered nut driver because of the
high volume assembly at a fixed location. These power tools have a
socket specifically designed to engage the body of the
connector.
A fastening tool, especially an power-driven one, easily can apply
an excessive amount of torque to the connector, thus damaging
either the wires or the connector. If cracks in the connector are
undetected, a short circuit could occur at the connection.
One solution to this problem was to limit the torque with a clutch
mechanism between the tool motor and the socket. However, torque
limiting devices add additional expense, size and weight to the
tool, and require adjustment to the optimum level for each specific
wiring application.
SUMMARY OF THE INVENTION
A general object of the present invention is to provide a manual or
power driven fastening tool for a twist-on wire connector.
Another object is to provide a wire connector fastening tool which
self-limits the amount of torque that can be applied to the
connector during the fastening operation.
These and other objectives are fulfilled by a system for joining
ends of electrical wires to a predefined torque level, which
comprises a twist-on connector and a tool socket specifically
designed to cooperate in limiting the amount of torque that the
socket is able to apply to the connector. The connector includes a
hollow body with an open end in which to receive the wires, a
closed end and an outer surface extending between the open and
closed ends. At least a portion of the outer surface has elements
which form a cross section with a polygonal shape. For example,
that portion of the body has side surfaces meeting at outside
corners to form a hexagonal cross section.
The tool socket includes a coupling by which torque is applied to
the tool socket by a driver. An aperture is provided in the tool
socket to removably receive the closed end of the connector with
side walls of the aperture engaging the portion of the connector's
outer surface. The aperture is significantly larger in cross
section than the connector so that a gap exists between the side
walls and the outer surface. For example, the aperture may have a
polygonal cross section with portions of the side walls between the
polygon corners being directed away from the connector to form the
gap. The gap results in the transfer of torque between the socket
and the connector being concentrated at the outside corners of the
connector. This torque concentration causes the elements of the
connector, such as the outside corners of the polygon, to deform
when the tool socket applies greater than the predefined torque
level to the connector. After that deformation, the socket turns
freely about the connector inhibiting additional torque from being
applied.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of a twist-on wire connector of a type
which can be used with the present invention;
FIG. 2 is an axial cross-sectional view through the wire connector
with a fastening socket attached thereto;
FIG. 3 is a transverse cross-sectional view along line 3--3 in FIG.
2 through the wire connector and the fastening socket assembly;
FIG. 4 is a transverse cross-sectional view through the wire
connector and the fastening socket after an excessive torque has
been applied;
FIG. 5 is a transverse cross-sectional through the wire connector
and a second embodiment of a fastening socket according to the
present invention;
FIG. 6 is a transverse cross-sectional through the wire connector
and a third embodiment of a fastening socket according to the
present invention; and
FIG. 7 is an axial cross-sectional view through the wire connector
with another type of fastening socket attached thereto.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, a twist-on wire connector 10 is formed of a
hollow body 12 having a general shape of a truncated cone. The body
12 preferably is formed of molded plastic and has an open end 14
which tapers to a smaller diameter closed end 15. As the outer
surface of the body 12 tapers toward the closed end 15, a
transition occurs to six flat surfaces 16. These flat surfaces 16
define a portion 17 of the body that has an equilateral hexagonal
cross-section for engagement by a wrench or socket for fastening
the connector 10. Although the exemplary wire connector 10 has a
hexagonal portion 17 various numbers of flat surfaces 16 may be
provided to form a body portion with different polygonal shapes for
tool engagement. Each flat surface 16 terminates at an edge 18 near
the closed end 15 and a conical tip extends from those edges at the
closed end.
The wire connector 10 also includes a pair of wings 20 which
project radially from the body adjacent open end 14. The radially
inner portion of the wings 20 provide exterior longitudinal
reinforcement thereby preventing the body 12 from collapsing. The
wire connector 10 is fastened onto wires by turning it in the
clockwise direction in the orientation illustrated. The curved
surface of each wing 20 has grooves which enable the fingers of a
user to grip the wire connector during the turning operation.
With reference to FIG. 2, the open end 14 of the wire connector has
a circular aperture 22 extending axially into the body 12 and
terminating a short distance from the closed end 15. The aperture
22 tapers in a narrowing manner reaching a shoulder 24
approximately one-third the depth of the aperture. The shoulder 24
defines an outer portion 26 of the aperture 22 and a smaller
diameter inner portion 28. A tapered coil spring 30 made of
electrically conductive metal is wedged into the smaller inner
portion 28.
In use, the stripped ends of two or more wires are inserted into
the aperture 22 at the open end 14 of the connector 10. The closed
end 15 of the connector then is placed into a hexagonal socket 32
attached to a square shaft 34 of an electrically or pneumatically
powered driver or a manual driver. The power tool then is activated
to rotate connector 10 which causes the threaded interior of the
aperture 22 to screw onto the stripped ends of the wires twistings
the wires together. When the wires have been twisted sufficiently
to assure a good electrical connection, the connector 10 is removed
from the socket 32. The wire connector remains on the ends of the
wires providing electrical insulation for the connection.
In the United States, the Underwriters Laboratory has specified
optimum torque levels for attaching different numbers and sizes of
electrical wires. Insufficient torque can result in a loose
connection which is susceptible to over-heating or disconnection,
while application of excessive torque can damage the wires or the
connector.
As previously noted, electrically or pneumatically powered tools
can apply an excessive amount of torque to the connector and break
the connector or the wires being fastened. As a consequence, the
combination of the wire connector 10 and the tool socket 32 is
specifically designed to cooperate and prevent an excessive amount
of torque from being applied. That design results in the sharply
angled outside corners 38 of the hexagonal connector portion 17
rounding at a predefined torque level allowing the socket 32 to
rotate freely about the connector body 12. Thereafter, torque is
not transferred to the connector 10 thus limiting the tool to
fastening the wire connector to no greater than the desired torque
limit. The yielding of the corners 38 on the connector body 12 not
only prevents excessive amount of torque from being applied, but
also ensures that the predefined torque level is applied as the
corners 38 do not yield until that level has been reached.
With reference to FIGS. 2 and 3, the tool socket 32 has a hexagonal
cross section aperture 36 within which the closed end 15 of the
connector 10 is removably received. The socket aperture 36 is
larger than the cross-sectional dimensions of the mating portion of
the connector 10 thus producing a loose fit as is particularly
evident in FIG. 3. As is apparent in this figure, the torque
exerted on the connector 10 by the socket 32 is concentrated at the
outside corners 38 of the hexagonal portion 17 of the connector. In
conventional fastening operations, it is desirable to have as tight
a fit as possible between the tool socket and the object between
fastening, in this case the connector 10. That tight fit assures
the torque will be distributed through a relatively large surface
contact area between the components and prevents the tool socket
from turning around the object. However, the present concept
intentionally provides less than the normally desired tight
fit.
The relatively loose fit between these components is sufficient to
for the tool socket 32 to rotate the connector 10 so as to properly
couple wires placed within the connector for fastening. When the
predefined torque level for the connection is reached, the angled
corners 38 of the hexagonal portion 17 of the plastic connector 10
become rounded as depicted in FIG. 4. That predefined torque level
is too intense for the relatively small amount of plastic material
at the connector corners 38 to withstand without deforming. The
deformation continues until the socket 32 is able to rotate freely
about the connector 10 at which time transfer of torque to the
connector ceases. The difference in cross sectional sizes of the
connector 10 and the socket aperture 22 and depth D (FIG. 2) that
the connector extends onto the socket aperture determine the area
of contact between those components and thus the torque magnitude
that must be applied before rounding occurs. The strength of the
plastic body 12 also is a factor in determining the torque level at
which corner rounding occurs. These factors enable the
socket-connector combination to be intentionally designed so that
the tool socket 32 can not exert more that the predefined torque
level on wire connector 10.
FIG. 5 illustrates an alternative design of a tool socket 40 which
has an aperture that is formed by six concave curved side walls 42.
The radius of each side wall is more than twice the distance to the
center axis 41 of the socket, for example. Adjacent side walls meet
at a line that is parallel to the center axis thus defining an
inside corner within which a corner 38 of the connector is
received. Because of the curving nature of the side walls, the
distance from the center axis 41 to the side walls is greatest at
each inside corner and decreases going from an inside corner toward
a midpoint 44 along each sidewall 42. Therefore, the hexagonal
cross-section portion 17 of the connector 10 is captivated in the
aperture so that rotation of the tool socket 40 by the square shaft
34 of the driver will produce rotation of the connector. However,
the torque being transferred to from the socket to the connector is
concentrated at each outside corner 38 which engages an inside
corner of the socket aperture. Thus when the predefined torque
limit for this type of connector is exceeded, the corners 38 round
allowing the socket to turn freely about the connector. The radius
of the side wall curvature defines the area of surface contact
between the tool socket 40 and the connector 10, and thus the
torque limit at which rounding occurs.
FIG. 6 illustrates a variation of the socket 40 in FIG. 5. In the
third embodiment, socket 50 has an aperture 52 with a dodecagon
cross section which by definition has twelve side surfaces and
twelve inside corners 54. The six outside corners 38 of the
hexagonal cross sectional portion 17 of the connector 10 nest
within six of the inside corners 54 with an open inside corner of
socket 50 between each inside corner 54 that is engaged by a
connector corner 38. The twelve side surfaces of the socket
aperture 52 angle away from the six exterior flat surfaces 16 of
the connector thus concentrating the applied torque to relatively
small surface areas of the connector adjacent to corners 38. This
causes the sharply angled connector corners 38 to round when the
predefined torque limit is exceeded.
Another version of a tool socket 60 according to the present
invention is shown in FIG. 7. This socket 60 has a hexagonal cross
section aperture 62 with a relatively large cross section portion
64 within which the closed end 15 of the connector 10 is removably
received. The aperture 62 narrows at a shoulder 66 against which
abut the edges 18 of the connector flat surfaces 16. The shoulder
66 defines the depth to which the connector 10 is able to enter the
aperture 62 and thus the amount of surface area in which the
connector contacts the socket. The torque transferred to the
connector 66 and thus the amount of surface area in which the
connector contacts the socket. The torque transferred to the
connector from the socket during the fastening operation in
concentrated in that contact surface area. Therefore by selectively
controlling that area with the depth of shoulder 66, the torque
level at which the corners of the hexagonal portion of the
connector become rounded can be set to the appropriate magnitude
for a given fastening operation.
In an variation of the socket 60 in FIG. 7, the portion 64 of
aperture 62 is so large in comparison to the cross section of the
connector 10 that the socket does not engage the connector flat
surfaces 16 or the corners at the meeting point of adjacent flat
surfaces. Instead the shoulder 66 has a curved projection which
extends into the notches 19 in the edges 18 of the flat surfaces
16. Thus torque is transferred from the socket to the connector
through the surfaces of the notches 19. The depth of the notches
defines the amount of surface area through which the torque is
transferred. By defining that surface area, a limit to the amount
of torque that may be applied to the connector can be established.
Application of a greater magnitude of torque causes the walls of
the notches to deform which results in the socket turning on the
end of the connector without further torque transfer.
* * * * *